Field of the Invention
The embodiments of the present invention relate to a molding machine and a driving method thereof.
Related Art
In injection molding, when a melted resin is filled at a high temperature in molds being in complete contact with each other, molecular orientation may occur in the resin. In such a case, a distortion may occur in a molded object. Therefore, in the injection molding, there is a case where an injection molding machine temporarily brings a moving mold into contact with a fixed mold and then slightly separates the moving mold from the fixed mold. After filling a resin in the molds, the injection molding machine performs an operation to bring the moving mold into close contact with the fixed mold. This prevents the molecular orientation from easily occurring in the resin and reduces a stress remaining in the molded object. Such an injection molding method is adopted particularly in foam molding.
Meanwhile, a toggle mechanism that operates a moving mold has a link mechanism including a plurality of links coupled to one another and a ball screw that operates the link mechanism. Therefore, there is play of toggle pins at link connection portions, play between grooves and threads of the ball screw, or the like as backlash or lost motion. The “play” leads to an error in the interval between the molds. Accordingly, at the time of injection molding, even when the injection molding machine intends to separate the moving mold from the fixed mold by a predetermined interval, there is a case where the moving mold is not separated from the fixed mold as expected due to the “play”. In this case, a resin pressure or a foam pressure is applied to the molds during injection of the resin and thus the moving mold is separated from the fixed mold during the injection of the resin. When the moving mold is displaced during the injection in this way, an expected resin amount or foam amount cannot be obtained, which increases the possibility that the molded object becomes defective.
The present invention has been achieved to solve the above problems and an object of the present invention is to provide a molding machine and a driving method thereof that can accurately control an opening amount of molds without requiring any special mechanism or apparatus to be added thereto.